This invention relates to a process for producing powder aggregate particle of polycarbonate resin from a solution of polycarbonate resin having a high molecular weight, that is, a viscosity average molecular weight of at least 70,000, and more particularly is a process for producing powder aggregate particle of high molecular weight polycarbonate resin having a large particle sizes and a high bulk density, free from fine powders, from a solution of high molecular weight polycarbonate resin.
The powder aggregate particle of high molecular weight polycarbonate resin produced according to the present invention can be readily dried and also readily handled in the molding, etc. The term "powder aggregate particle" used herein refers to porous particle comprised of an aggregate of powder formed by precipitation. The high molecular weight polycarbonate resin is useful for producing films.
Solidification of polycarbonate resin from a polycarbonate resin solution can be carried out by adding a non-solvent to the polycarbonate resin solution to precipitate the polycarbonate resin (precipitation procedure) or by distilling out a solvent from the polycarbonate resin solution, thereby concentrating the solution to obtain powder (concentration procedure). However, high molecular weight polycarbonate resin having viscosity average molecular weight of at least 70,000, that is a higher molecular weight than that of the ordinary polycarbonate resin, cannot be solidified satisfactorily by these procedures. For example, in the precipitation procedure the solidified polycarbonate resin undergoes leather like surface formation i.e. formation of leather like surface of solidified polycarbonate resin on the outside of solvent droplets, unless the polycarbonate resin solution is at a very low concentration. When the polycarbonate resin solution is at an extremely low concentration, not only the solvent must be used in a large amount, but also the solidified polycarbonate resin turns fine powder. On the other hand, in the concentration procedure to distill out the solvent from the solution the solidified polycarbonate resin undergoes leather like surface formation or turns sticky masses, which will turn into a fiber state by crushing.
Japanese Patent application Kokai (Laid-open) No. 61-250026 discloses a process for the solidification of a polycarbonate resin solution having a 10 to 25% by weight of polycarbonate resin by adding a poor solvent to the solution and pouring the resulting mixture into warm water, but it has been found that high molecular weight polycarbonate resin cannot be solidified satisfactorily.